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Abstract
Beneficial effect of plants in treatment of diabetes is well-known in traditional medicine and confirmed in numerous scientific studies. The basic platform for testing potential antidiabetic activity of traditionally known plants and their bioactive compounds are experiments in vitro. These assays usually measured enzyme inhibitory activity such as ±-amylase and ±-glucosidase controlling starch breakdown and other aspects connected with diabetes mellitus disease. In recent years the interest in plant-derived compounds useful in diabetes treatment or complication reduction is in great expansion. The main goal leads to establish a mechanism of action of plant extracts or active compounds for finding novel antidiabetic drug with as less toxicological properties. The aim of this work is data collection and discussing the newest result in area of plant extracts, compounds and their antidiabetec effects using in vitro models. The data covered in this review are include plant extract, compounds polyphenols, terpenoids, indicating that some of less known plants and isolated new compounds might be a promising source for treatment and prevention of diabetes mellitus.
INTRODUCTION
Diabetes mellitus (DM), known as diabetes, is serious metabolic disease that occurs due to insulin secretion disorders, its inefficiency or both. Uncontrolled hyperglycemia, in time, caused serious health complications to the heart, blood vessels, eyes, kidneys and nerves. The most common type of diabetes in world is type 2, which is characterized by insulin resistance or insulin relatively deficiency (WHO, 2016). The fact that this disease became more ubiquitous in developing countries with estimation that the number of patients with diabetes it is hard to count, because it takes a years before complete diagnosis. Different data occurs, and the estimation is that in 2030. number of patients with DM disease will be over 366 or even 592 million, which is for serious concern (Malviya et al., 2010., Wang et al, 2017). In focus of many researchers groups is the idea to testing plants which are recognized in treatment of diabetes in traditional medicine of different countries. Some sources recognized even 800 plant species to have importance in treatment of DM, while for 108 plants was found that could delay disease occurrence or correct the disturbed metabolism (Mamun-or-Rashid et al, 2014). Plant organs contain different bioactive compounds which could be extracted by various solvents and types of extractions from row or dry material and tested. Plant extracts or isolated plant compounds are of great importance regardless which they active against symptoms or could be efficient in diabetes prevention or complication caused by DM reduction. Intensively searching for finding new more effecting drugs are based on experience of traditional medicine knowledge. Importance of traditional medicine in antidiabetic purpose is connected with reparation effect to pancreas tissue to produce enough insulin or inhibit intestinal absorption of glucose (Malviya et al., 2010). Besides extracts efficiency and mechanism of action its safety is required.
The first step of testing potential antidiabetics from plants includes in vitro tests. Methods which are used in vitro are mostly based on potential inhibition activity of enzymes caused by compounds present in plant extracts. Intestinal enzymes, ±-amylase and ±-glucosidase are involved in carbohydrate metabolism. ±amylase (±-1,4-glucan-4-glucanohydrolase), is an enzyme produced in saliva and by pancreas catalyzes the hydrolysis of starch. Enzyme ±-glucosidase, regulate digestion of oligosaccharides to glucose (Lin et al., 2016). Spectrophotometric methods are useful tool used for measuring the inhibition of carbohydrate digesting enzyme (±-amylase, ±-glucosidase, sucrase), dipeptidyl peptidase IV (DPP IV), protein tyrosine phosphatase 1B (PTP 1B), as well as to measure glucose uptake assays using dialysis bag. The yeast cells are convenient for measuring the hemoglobin glycosylation and glucose transport thro yeast cell membrane as well as cell lines such as pancreatic Rat insulinoma cells (RIN m5F cells), ² cell line, 3T3 L1 cells, etc.) (Dsouza and Lakshmidevi, 2015). ±-amylase inhibition performed using different assays such as starch iodine method, 3, 5-Dinitrosalicylic acid method (DNSA) or glucose-stimulated insulin secretion (GSIS assay), as well as glucose transport inhibition assay were used for validation of plant extracts activity (Kumar et al., 2013; Wang et al, 2018). The synthetic hypoglycemic agents which act as the enzymes inhibitors which are in clinical use are acarbose, miglitol and voglibose. These drugs are with limited effects and produce serious side effects (Kumar et al., 2018).
Secondary metabolites isolated from plants such as alkaloids, terpenoids, cartenoids, glycosides, phenols, etc. (Malviya et al., 2010)., tannins, flavonoids, C and E vitamins are were found to possess antidiabetec effects and ability to maintain ²-cells performance and decrease glucose levels in the blood (Kooti et al, 2016).
LITERATURE SEARCH AND SELECTION CRITERIA
All necessary information for this review are collected in the period of the January 1st 2014 and December 31st 2018. The keywords: plant, extract, antidiabetic and in vitro are used for that. The main criteria for articles selection was plants and their isolated compounds which have antidiabetic activity using in vitro models. Review also includes studies with pure compounds, as well as extracts, fractions or mixture of compounds without testing isolated compounds. The table were used for analyzing collected data from relevant articles (Table 1). The information were statistically processed and explained.
RESULTS
Geographical origin of plants
The base of Indian and Chinese traditional medicine is usage a lot of plants in treatments for many disease [2]. This usage dated over 1000 years ago and represent important sources for the development of antidiabetic drugs [510]. Accordingly, most of the tested plants in our research were from India (24.2%) and China (22.6%), followed by Nigeria (6.5%), Mexico (4.8%), Korea, Malaysia, South Africa, Turkey, United States and Vietnam (3.2%), South Africa, Algeria, Bosnia and Herzegovina, Brazil, Cuba, Ecuador, Eritrea, France, Indonesia, Italy, Ivory Coast, Peru, Sri Lanka and Tunisia (1.6%).
Plants families and genera
In this manuscript, we analyzed 41 families and 68 species with antidiabetic activity. The most frequently was Fabaceae family with 12.1%, followed by Asteraceae (10.6%), Arecaceae, Meliaceae and Moraceae (4.5%), Apiaceae, Apocynaceae, Lamiaceae, Mimosaceae, Myrtaceae and Solanaceae (3.0%), Acanthaceae, Adoxaceae, Anacardiaceae, Ascelpediaceae, Betulaceae, Burseraceae, Caprifoliaceae, Cucurbitaceae, Euphorbiaceae, Fagaceae, Hypericaceae, Malvaceae, Melastomataceae, Musaceae, Phyllanthaceae, Platanaceae, Poaceae, Polygalaceae, Polygonaceae, Punicaceae, Rosaceae, Rubiaceae, Rutaceae, Sapindaceae, Sapotaceae, Sterculiaceae, Symplocaceae, Theaceae, Zingiberaceae and Zygophyllaceae (1.5%).
The genera most studied in the selected articles were Achillea, Ficus and Momordica with 2.9%. All other analyzed genera were present with 1.5% (Acacia, Albizzia, Allophyllus, Arctium, Artemisia, Astragalus, Azadirachta, Betula, Brachylaena, Calotropis, Camellia, Capsicum, Caralluma, Chrysophyllum, Chukrasia, Cicer, Cocos, Coriandrum, Crotalaria, Cyclopia, Dacryodes, Dalbergia, Derris, Eugeissona, Euphorbia, Grewia, Hamelia, Hedychium, Hypericum, Khaya, Lonicera, Meriandra, Miconia, Morus, Muehlenbeckia, Musa, Parkia, Phoenix, Phyllanthus, Physalis, Pistacia, Pithecellobium, Platanus, Plectocomiopsis, Psiadia, Psidium, Pterospermum, Punica, Quercus, Rosa, Ruellia, Sarcostemma, Scutellaria, Securidaca, Sphallerocarpus, Symplocos, Syzygium, Taraxacum, Tribulus, Viburnum, Zanthoxylum and Zea.
Plant parts
Ethnopharmacological knowledge about using different parts of plants represent base for choosing plant material for extraction and isolation of chemical compounds with antidiabetic activity (Munhoz and Frode, 2018). In the present study, 32.4% used leaves for the isolation of active compounds, followed by aerial parts (16.2%), fruits (9.5%), roots and stems (6.8%), seeds and stem bark (5.4%), flower buds, flowers, fruit coat, fruit peel, heartwood, husk fiber, palm hearts, rhizomes, root bark, corn silk and trunk bark (1.4%).
Solvent used for extraction
Variation in extract activity has caused by solvent polarity as its major factor (Mateji et al., 2018). The most used solvent in the selected articles were polar solvents: water (20.6%), methanol and ethanol (16.8% and 16.0%, respectively) and non-polar solvent (ethyl acetate 14.5%). Also, they utilized hexane (8.4%), dichloromethane (4.6%), acetone (3.1%), n-butanol (2.3%), chloroform (1.5%), petroleum ether (0.8%), solvent mixture like hydro alcohol (1.5%), hydro methanol (0.8%), acid-ethanol (0.8%) and different fraction for isolation active compound (ethyl acetate, n-butanol, hexane and water 1.5% and chloroform, ethanol and anthocyanin-rich fraction 0.8%).
In vitro Models of DM
The very important instrument for screening activity in bioassay studies and detail explanation the mechanism of action of an active compound is in vitro model for evaluating new antidiabetic compounds.
Determining the action mechanism of new drugs is done using a lot of enzymes. When investigating antidiabetic action, different extracts were most commonly tested against ±-glucosidase activity (56.5%), followed by inhibition of ±-amylase (32.9%), PTP1B (7.1%), ²-glucosidase, lipase and DPP-4 (1.2%).
The common for screening and evaluating the compound mechanism of action in in vitro tests is the analysis of enzymes [20]. The most prevalent cell lines identified in the present review were 3T3-L1 (30.4%), L6 (26.1%), HepG2 (13.0%), C2C12 and BRIN BD11 (8.7%), H4IIE, AML12 and INS-1 (4.3%) cells.
Antidiabetic Compounds Isolated from Plants
In the present review, 42 compounds group were found to have antidiabetic activity. The most frequently were flavonids (23.4%), followed by phenolic acids (8.9%), phenols and tannins (6.5%), saponins and triterpenoid (4.8%), flavonoid glycosides (4.0%), phytosterols, terpenoid and alkaloids (3.2%), carbohydrate and fatty acids (2.4%), limonoids, protein and steroidal (1.6%), acetate, anthocyanin, anthraquinones, benzyl alcohol, caffeoylquinic acids, cardiac glycosides, carotenoids, catechin, chlorins, cholesterol, chromones, coumarins, curcuminoids, diterpene alcohol, ester, ethyl ester, flavones, heteropolysaccharide, indole alkaloid, ketones, lignans, lipid, monosaccharides, sterols, terpenic lactones, tetranortriterpenoid and triterpenic acid (0.8%).
DISCUSSION
Antidiabetic Activity of Plants extracts
The most powerful plants which are officially recognized and supported by clinical evidence, are Ocimum tenuiflorum L., leaves and Trigonella foenum-graecum L., seed (Governa et al, 2018). Current research represent antidiabetic agents obtained from seed extract from Trigonella foenum-graecum FenfuroTM, CR0010810 which have promising activity and now is during clinical trials for human uses (Swaroop et al., 2018). The major compound of the seed fiber of fenugreek with antidiabetec potential is galactomannan Singab et al., 2014. Leaves of Ocimum tenuiflorum contains high amount of eugenol, ursolic acid, flavonoids (orientin and vicenin) and many phenolic compounds which contribute to biological activities including antidiabetic (Parasuraman et al, 2015). Traditional uses of well-known plant Allium cepa L. all over the world ratify its medicinal benefit. Its bulbs are rich in sulphur amino acids, flavonoids (flavonols and anthocyanin), phytosterols and saponin possessed different biological activities. Flavonoid alliuocide G showed in vitro ±-amylase inhibitory activity (Marrelli et al, 2019). Apart from these plants, World Health Organization (WHO) monographs showed plants and their vegetative or reproductive organs with antidiabetec activity described in Pharmacopoeias of different countries such as Azadirachta indica A. Juss. (Meliaceae), Momordica charantia L. (Cucurbitaceae), Panax ginseng C.A. Meyer, P. quinquefolius L. (Araliaceae) and Rehmannia glutinosa (Gaertn.) DC. (Scrophulariaceae) (Governa et al, 2018).
In study of Vijayalakshmi et al., 2018, in vitro glucose uptake activities of the methanol extract of Sarcostemma brevistigma were examined using 3T3L1 cell lines. It was found that considerably higher glucose uptake activity of 38.04% which is equivalent to the glucose uptake shown by 100 nm insulin (40.10%).
Hyperglycemic activity from aerial part of methanolic, water and hydro methanolic extracts of Caralluma umbellata were analyses by Bellamakondi et al., 2014. The methanolic extract was found to have significant glucose uptake. Further, this extract was also found to have promising role in inhibiting alpha amylase and pancreatic lipase. The results show that Caralluma umbellata has potential antidiabetic property.
The antidiabetic effect of hydroalcoholic extract of aerial parts Achillea millefolium was evaluated by Chávez-Silva et al., 2018. Extract promoted the ±-glucosidases inhibition by 55% at 1 mg/ml respect to control. On the other hand, extract increased the PPAR³ (five-times) and GLUT4 (two-fold) relative expression than control.
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